EFFECTS OF SODIUM CHLORIDE CONCENTRATIONS ON ZETA POTENTIALS OF CLAY MINERALS ESTIMATED BY AN ELECTROKINETIC SONIC AMPLITUDE METHOD

The absolute values of zeta (ζ) potentials estimated by an electrokinetics sonic amplitude (ESA) method decreased gradually with the increase of NaCl concentration below the flocculation value of 1.5×10-2 and 1.5×10-3 mol L-1 in the suspension of montmorillonite at pH 8 and allophane at pH 7.5 respectively. Theζ potentials increased inversely above the flocculation values. The absolute value of potential in kaolinite suspension at pH 6 was found to decrease even above its flocculation value, and increased inversely above 5.6×10-3 mol L-1 NaCl. The flocs already began to form below the fl occulation value in the montmorillonite suspension at pH 8, but the formation and precipitation of the fl ocs began almost simultaneously in the kaolinite suspension at pH 6. Theζ potential of allophane at pH 3.5 began to increase at about 1.5×10-3 mol L-1 NaC1, which coincided with the absolute value at pH 7.5. The flocs in the allophane suspension at pH 3.5 began to form at near 2×10-3 mol L-1 NaC1, but to precipitate above 5×10-3 mol L-1 NaCl. The aspects of flocs formation in allophane were a little different from montmorillonite and kaolinite.